Phonatory characteristics of the excised human larynx in comparison to other species

Nonlinear Elasticity of Blood Vessels and Vascular Grafts

The transplantation of vascular grafts has emerged as a prevailing approach to address vascular disorders. However, the development of small-diameter vascular grafts is still in progress, as they serve in a more complicated mechanical environment than their counterparts with larger diameters. The biocompatibility and functional characteristics of small-diameter vascular grafts have been well developed; however, mismatch in mechanical properties between the vascular grafts and native arteries has not been accomplished, which might facilitate the long-term patency of small-diameter vascular grafts. From a point of view in mechanics, mimicking the nonlinear elastic mechanical behavior exhibited by natural blood vessels might be the state-of-the-art in designing vascular grafts. This review centers on elucidating the nonlinear elastic behavior of natural blood vessels and vascular grafts. The biological functionality and limitations associated with as-reported vascular grafts are meticulously reviewed and the future trajectory for fabricating biomimetic small-diameter grafts is discussed. This review might provide a different insight from the traditional design and fabrication of artificial vascular grafts.

Excised human larynx in N-vinyl-2-pyrrolidone-embalmed cadavers can produce voiced sound by pliable vocal fold vibration

Tissue-hardening effect and health-hazard issue of formaldehyde (FA) have long been a great disadvantage of this conventional fixative in anatomical research. We recently developed a FA-free embalming method for cadavers which utilizes N-vinyl-2-pyrrolidone (NVP) and enables assessment of motion kinetics by maintaining the softness of embalmed tissue. By assessing the feasibility of NVP-embalmed tissue to mimic vocalization, this study aimed to prove the potential of embalmed cadavers, which have previously been used only for the understanding of anatomical morphology, for the assessment of precise motion physiology in the human body. Ten cadavers embalmed in NVP (n = 6) and FA (n = 4) were incorporated in this study. Excised larynges underwent experimental phonation to mimic vocalization with fast and pliable vibration of vocal folds. High-speed digital imaging was utilized for the assessment of vocal fold vibration. Furthermore, acoustic analysis of the voiced sound, and reproducibility examination were also performed. Regular vocal fold vibrations successfully produced voiced sounds during experimental phonation using NVP-embalmed larynges. The vibratory frequency, vibration amplitude, and stretch rate of the vocal folds were comparable to those of living humans. Six months after the first experiment, the vocal parameters were reproduced, to suggest the long-term preservation potential of our NVP-embalming technique. On the other hand, neither voiced sound nor vocal fold vibration were observed in FA-embalmed larynges. This novel embalming technique could pioneer the next era to utilize embalmed cadavers for the examination of motion physiology in the human body.

Anterior glottoplasty: the effect of inclusion of the vocal fold lamina propria to frequency elevation

BACKGROUND

Anterior glottoplasty is a commonly used treatment for voice feminization. But it remains in dispute over whether to suture of the ligament as part of the procedure.

OBJECTIVES

This study aimed to explore the effect of inclusion of the vocal lamina propia.

MATERIAL AND METHODS

Anterior webs were created in 8 excised canine larynges by sutures placed at 10%, 20%, and 30% of the vocal fold length, respectively. The suture depth was divided into two groups: epithelium layer (Shallow Suture, SS group) and deep layers of vocal fold lamina propia (Deep Suture, DS group).

RESULTS

For anterior webs between 0% and 30%, the frequency elevation ranged from 3% to 151% of the pre-web fundamental frequency (fo) in SS group and from 13% to 222% in DS group. No significance was found between two groups at three different sutures (p = .486 for suture at 10% of vocal fold length, 0.686 for 20%, 0.886 for 30%, respectively).

CONCLUSIONS AND SIGNIFICANCE

The frequency in excised canine larynx increased continuously as the anterior glottic webs ranged from 0% to 30%. The inclusion of the vocal fold lamina propia does not affect the frequency elevation.

Phase-averaged and cycle-to-cycle analysis of jet dynamics in a scaled up vocal-fold model

Phase-averaged and cycle-to-cycle analysis of key contributors to sound production in phonation is examined in a scaled-up vocal-fold model. Simultaneous temporally and spatially resolved pressure and velocity measurements permitted examination of each term in the streamwise integral momentum equation. The relative sizes of these terms were used to address the issue of whether transglottal pressure is a surrogate for vocal-fold drag, a quantity directly related to sound production. Further, time traces of transglottal pressure and volume flow rate provided insight into the role of cycle-to-cycle variations in voiced sound production which affect voice quality. Experiments were conducted using a 10× scaled-up model in a free-surface water tunnel. Two-dimensional vocal-fold models with semi-circular ends inside a square duct were driven with constant opening and closing speeds. The time from opening to closed, T_o , was half the oscillation period. Time-resolved digital particle image velocimetry (DPIV) and pressure measurements along the duct centreline were made for 3650 ≤ Re ≤ 8100 and equivalent life frequencies from 52.5 to 97.5 Hz. Results showed that transglottal pressure does serve as a surrogate for the vocal-fold drag. However, smaller but non-negligible momentum flux and inertia terms, caused by the jet and vocal-fold motions, may also contribute to vocal-fold drag. Further, cycle-to-cycle variations including jet switching and modulation are inherent in flows of this type despite their high degrees of symmetry and repeatability. The origins of these variations and their potential role in sound production and voice quality are discussed.

A one-dimensional flow model enhanced by machine learning for simulation of vocal fold vibration

A one-dimensional (1D) unsteady and viscous flow model that is derived from the momentum and mass conservation equations is described, and to enhance this physics-based model, a machine learning approach is used to determine the unknown modeling parameters. Specifically, an idealized larynx model is constructed and ten cases of three-dimensional (3D) fluid-structure interaction (FSI) simulations are performed. The flow data are then extracted to train the 1D flow model using a sparse identification approach for nonlinear dynamical systems. As a result of training, we obtain the analytical expressions for the entrance effect and pressure loss in the glottis, which are then incorporated in the flow model to conveniently handle different glottal shapes due to vocal fold vibration. We apply the enhanced 1D flow model in the FSI simulation of both idealized vocal fold geometries and subject-specific anatomical geometries reconstructed from the magnetic resonance imaging images of rabbits' larynges. The 1D flow model is evaluated in both of these setups and shown to have robust performance. Therefore, it provides a fast simulation tool that is superior to the previous 1D models.

Effect of Ventricular Folds on Vocalization Fundamental Frequency in Domestic Pigs (Sus scrofa domesticus)

This study investigates the effect of the ventricular folds on fundamental frequency (f_o) in the voice production of domestic pigs (Sus scrofa domesticus). The excised larynges of six subadult pigs were phonated in two preparation stages, with the ventricular folds present (PS1) and removed (PS2). Vocal fold resonances were tested with a laser vibrometer, and a four-mass computational model was created. Highly significant f_o differences were found between PS1 and PS2 (means at 93.7 and 409.3 Hz, respectively). Two tissue resonances were found at 115 Hz and 250-290 Hz. The computational model had unique solutions for abducted and adducted ventricular folds at about 150 and 400 Hz, roughly matching the f_o measured ex vivo for PS1 and PS2. The differing f_o encountered across preparation stages PS1 and PS2 is explained by distinct activation of either a high or a low eigenfrequency mode, depending on the engagement of the ventricular folds. The inability of the investigated larynges to vibrate at frequencies below 250 Hz in PS2 suggests that in vivo low-frequency calls of domestic pigs (pre-eminently grunts) are likely produced with engaged ventricular folds. Allometric comparison suggests that the special, mechanically coupled "double oscillator" has evolved to prevent signaling disadvantages. Given these traits, the porcine larynx might - apart from special applications relating to the involvement of ventricular folds - not be an ideal candidate for emulating human voice production in excised larynx experimentation.

Preclinical Performance Evaluation of a Robotic Endoscope for Non-Contact Laser Surgery

Despite great efforts, transoral robotic laser surgery has not been established clinically. Patient benefits are yet to be proven to accept shortcomings of robotic systems. In particular, laryngeal reachability and transition from microscope to accurate endoscopic laser ablation have not been achieved. We have addressed those challenges with a highly integrated robotic endoscope for non-contact endolaryngeal laser surgery. The current performance status has been assessed in multi-level user studies. In addition, the system was deployed to an ex vivo porcine larynx. The robotic design comprises an extensible continuum manipulator with multifunctional tip. The latter features laser optics, stereo vision, and illumination. Vision-based performance assessment is derived from depth estimation and scene tracking. Novices and experts (n = 20) conducted teleoperated delineation tasks to mimic laser ablation of delicate anatomy. Delineation with motion-compensated and raw endoscopic visualisation was carried out on planar and non-planar nominal patterns. Root mean square tracing errors of less than 0.75 mm were feasible with task completion times below 45 s. Relevant anatomy in the porcine larynx was exposed successfully. Accuracy and usability of the integrated platform bear potential for dexterous laser manipulation in clinical settings. Cadaver and in vivo animal studies may translate ex vivo findings.

A reduced-order flow model for vocal fold vibration: from idealized to subject-specific models

We present a reduced-order model for fluid-structure interaction (FSI) simulation of vocal fold vibration during phonation. This model couples the three-dimensional (3D) tissue mechanics and a one-dimensional (1D) flow model that is derived from the momentum and mass conservation equations for the glottal airflow. The effects of glottal entrance and pressure loss in the glottis are incorporated in the flow model. We consider both idealized vocal fold geometries and subject-specific anatomical geometries segmented from the MRI images of rabbits. For the idealized vocal fold geometries, we compare the simulation results from the 1D/3D hybrid FSI model with those from the full 3D FSI simulation based on an immersed-boundary method. For the subject-specific geometries, we incorporate previously estimated tissue properties for individual samples and compare the results with those from the high-speed imaging experiment of in vivo phonation. In both setups, the comparison shows good agreement in the vibration frequency, amplitude, phase delay, and deformation pattern of the vocal fold, which suggests potential application of the present approach for future patient-specific modeling.

Contact Pressure Between the Vocal Folds in Reinke's Edema: Experimental Observations on an Excised Human Larynx

OBJECTIVE

To analyze the range of values of the contact pressure between the membranous vocal folds with Reinke's edema and to compare it to those observed in the absence of such a lesion.

METHODS

Two human larynges were separately tested on the experimental bench, one of them with a bilateral loose swelling of the vocal folds. Once in a glottal prephonatory configuration, airflow was increased until achievement of self-sustained oscillations while recording aerodynamic, acoustic, electroglottographic data, and contact pressure between the folds.

RESULTS

We observed well-documented variations in acoustical parameters, as the decrease of the fundamental frequency and the increase of the phonation threshold pressure. The results of the study also point to a significant increase in the amplitude of the contact pressure in presence of the Reinke's edema, and a lower degree of harmonicity of the produced sounds.

CONCLUSION

This is the first report of ex vivo study of a larynx with Reinke's edema. It highlights the increase in the contact pressure during phonation, which possibly contributes to sustain the lesion once it appeared.

Effects of Angle of Epiglottis on Aerodynamic and Acoustic Parameters in Excised Canine Larynges

OBJECTIVES

The aim of this study is to explore the effects of the angle of epiglottis (Aepi) on phonation and resonance in excised canine larynges.

METHODS

The anatomic Aepi was measured for 14 excised canine larynges as a control. Then, the Aepis were manually adjusted to 60° and 90° in each larynx. Aerodynamic and acoustic parameters, including mean flow rate, sound pressure level, jitter, shimmer, fundamental frequency (F0), and formants (F1'-F4'), were measured with a subglottal pressure of 1.5 kPa. Simple linear regression analysis between acoustic and aerodynamic parameters and the Aepi of the control was performed, and an analysis of variance comparing the acoustic and aerodynamic parameters of the three treatments was carried out.

RESULTS

The results of the study are as follows: (1) the larynges with larger anatomic Aepi had significantly lower jitter, shimmer, formant 1, and formant 2; (2) phonation threshold flow was significantly different for the three treatments; and (3) mean flow rate and sound pressure level were significantly different between the 60° and the 90° treatments of the 14 larynges.

CONCLUSIONS

The Aepi was proposed for the first time in this study. The Aepi plays an important role in phonation and resonance of excised canine larynges.

Aeroacoustic source characterization in a physical model of phonation

This paper presents measurements conducted in a physical model of the adult human airway. The goals of this work are to (1) benchmark the physical model to excised larynx models in the literature and (2) empirically demonstrate the relationship between vocal fold drag and sound production. Results from the airway model are first benchmarked to published time-averaged behavior of excised larynx models. The airway model in this work exhibited higher glottal volume flow, lower glottal resistance, and less fundamental frequency variation than excised larynx models. Next, concurrent measurements of source behavior and radiated sound were compared. Unsteady transglottal pressure (a surrogate measure for vocal fold drag) and radiated sound, measured at the mouth, showed good correlation. In particular, the standard deviation and the ratio of the power of the first and second harmonics of the transglottal and mouth pressures were strongly correlated. This empirical result supports the assertion that vocal fold drag is the principal source of sound in phonation.

Juvenile Ovine Ex Vivo Larynges: Phonatory, Histologic, and Micro CT Based Anatomic Analyses

It is well known that the phonatory process changes during the life span. However, detailed investigations on potential factors concerned are rare. To deal with this issue, we performed extended biomechanical, macro anatomical, and histological analyses of the contributing laryngeal structures in ex vivo juvenile sheep models. Altogether twelve juvenile sheep larynges were analyzed within the phonatory experiments. Three different elongation levels and 16 different flow levels were applied to achieve a large variety of phonatory conditions. Vocal fold dynamics and acoustical and subglottal signals could be analyzed for 431 experimental runs. Subsequently, for six juvenile larynges microcomputed tomography following virtual 3D reconstruction was performed. The remaining six juvenile larynges as well as six ex vivo larynges from old sheep were histologically and immunohistologically analyzed. Results for juveniles showed more consistent dynamical behavior compared to old sheep larynges due to vocal fold tissue alterations during the life span. The phonatory process in juvenile sheep seems to be more effective going along with a greater dynamic range. These findings are supported by the histologically detected higher amounts of elastin and hyaluronic acid in the lamina propria of the juvenile sheep. The 3D reconstructions of the thyro-arytenoid muscles (TAM) showed a symmetrical shape. Intraindividual volume and surface differences of the TAM were small and comparable to those of aged sheep. However, TAM dimensions were statistically significant smaller for juvenile larynges. Finally, topographical landmarks were introduced for later comparison with other individuals and species. This work resulted in detailed functional, immunohistological, and anatomical information that was not yet reported. This data will also provide reference information for therapeutic strategies regarding aging effects, e.g. laryngeal muscle treatment by functional electrical stimulation.

Development of Excised Larynx

The larynx is a complex organ which has a role in a variety of functions such as phonation, breathing, and swallowing. To research these functions, it is widely accepted that in vivo studies provide more anatomically and physiologically relevant findings. However, invasive procedures are generally needed to measure variables such a subglottal pressure, vocal fold tension and stiffness, and cricothyroid muscle stretch. Performing studies using excised larynges is a useful technique which makes it possible to not only measure phonation parameters but control them as well. Early studies using excised larynges mainly focused on controlling specific parameters and mathematical modeling simulations. The use of these studies has helped further research in laryngeal anatomy, imaging techniques, as well as aerodynamic, acoustic, and biomechanical properties. Here, we describe the progress of this research over the past 5 years. The number of accepted animal models has increased and ideas from excised larynx studies are starting to be applied to treatment methods for laryngeal disorders. These experiments are only valid for an excised situation and must continue to be combined with animal experimentation and clinical observations.

Phonation Analysis Combined with 3D Reconstruction of the Thyroarytenoid Muscle in Aged Ovine Ex Vivo Larynx Models

OBJECTIVE

The aim of the study was to establish a basic data set of combined functional and anatomical measures of aged sheep larynges using ex vivo models. Combining these two approaches in one and the same larynx is an unmet goal so far yet is important as newer treatment strategies aim to preserve the organ structure and new assessment tools are required. Ovine larynges were used as their dimensions, and muscle fiber type distribution highly resemble the human larynx.

STUDY DESIGN

Ex vivo animal study.

METHODS

Larynges of six sheep (~9 years of age) were subjected to ex vivo functional phonatory experiments. Phonatory characteristics were analyzed as a function of longitudinal vocal fold (VF) prestress. Anatomical measurements of the same larynges comprised micro-computed tomography scans followed by three-dimensional (3D) reconstructions. Using specially adapted radiological scan protocols with subsequent 3D reconstruction, muscle volumes, surface areas, and anatomical measurements were computed.

RESULTS

Increasing longitudinal prestress yielded higher subglottal pressure (P_S) for the same airflow. Quantitative differences to previous studies-such as the increased P_S and increased phonation threshold pressure-were detected. We achieved excellent visualization of the laryngeal muscles and framework, resulting in accurate 3D reconstructions for quantitative analysis. We found no significant intraindividual volume differences of the thyroarytenoid muscles.

CONCLUSION

The established protocol allows precise functional and anatomical measures. The data created provide a reference data set for upcoming therapeutic strategies (eg, growth factor therapy, functional electrical stimulation) that target essential structures of the VFs such as the laryngeal muscles and/or the VF mucosa.

Establishment and Analysis of False Vocal Folds Hypertrophy Model in Excised Canine Larynges

OBJECTIVE

This study aimed to investigate the role of false vocal folds (FVFs) medialization in phonation and the acoustic impact of ventricular hypertrophy by establishing an FVF hypertrophy model.

STUDY DESIGN

A prospective in vitro experiment was carried out.

SETTING

The study was carried out using a pseudolung platform with high-speed camera in a soundproof room.

MATERIALS AND METHODS

Control, degree I, and degree II FVFs hypertrophy were simulated in 10 excised larynges via fructose injection of 0.1 mL for degree I and 0.25 mL for degree II. Mean flow rate (MFR), fundamental frequencies (F0), formants, and sound pressure level were measured with a subglottal pressure of 1.5 kPa and 2.5 kPa, respectively.

RESULTS

When the subglottal pressure was controlled at both at 1.5 kPa and at 2.5 kPa, the degree of FVF hypertrophy significantly influenced the distribution of the formants, F0, and MFR in excised canine larynges. Increasing the degree of hypertrophy was associated with a decrease in F0 and an increase in MFR. In degree II FVF hypertrophy models, the sound pressure level and the first formant were significantly higher (P < 0.05) than in normal models.

CONCLUSION

Hypertrophy of the FVFs has a significant influence on the distribution of sound energy and is associated with changes in sound quality.

What Can be Learned from the Time Course of Changes in Low-Frequency Stimulated Muscle?

Not available.

Automated setup for ex vivo larynx experiments

Ex vivo larynx experiments are limited in time due to degeneration of the laryngeal tissues. In order to acquire a significant and comparable amount of data, automatization of current manual experimental procedures is desirable. A computer controlled, electro-mechanical setup was developed for time-dependent variation of specific physiological parameters, including adduction and elongation level of the vocal folds and glottal flow. The setup offers a standardized method to induce defined forces on the laryngeal cartilages. Furthermore, phonation onset is detected automatically and the subsequent measurement procedure is automated and standardized to improve the efficiency of the experimental process. The setup was validated using four ex vivo porcine larynges, whereas each validation measurement series was executed with one separate larynx. Altogether 31 single measurements were undertaken, which can be summed up to a total experimental time of about 4 min. Vocal fold elongation and adduction lead both to an increase in fundamental frequency and subglottal pressure. Measurement procedures like applying defined subglottal pressure steps and onset-offset detection were reliably executed. The setup allows for a computer-based parameter control, which enables fast experimental execution over a wide range of laryngeal configurations. This maximizes the number of measurements and reduces personal effort compared with manual procedures.

Parameters From the Complete Phonatory Range of an Excised Rabbit Larynx

OBJECTIVE

This study aims to collect data throughout the complete phonatory range using rabbit larynges.

STUDY DESIGN

This is a methodological excised rabbit larynx study.

METHODS

Seven rabbit larynges were dissected and mounted on a modified excised laryngeal apparatus. Phonation was initiated at phonation threshold pressure (PTP) and airflow was increased by consistent increments until phonation instability pressure (PIP) was reached. At each airflow level, aerodynamic measurements, acoustic recordings, and high-speed videos were recorded. This procedure was repeated at multiple elongation conditions to further explore the parameters. Data were then compared across subjects and elongation conditions.

RESULTS

At PTP, subglottal pressure, fundamental frequency, and sound pressure level were found to increase significantly as elongation was increased. As elongation was increased at PIP, airflow was found to significantly decrease, whereas fundamental frequency was found to significantly increase. Vibratory amplitude decreased at both PTP and PIP as elongation increased. Also, as elongation increased, the range of all parameters was found to decrease significantly.

CONCLUSIONS

The results obtained, combined with the similarities of the histologic structure of the vocal fold lamina propria between rabbits and humans, validate the rabbit larynx as an effective and reliable model for tissue inflammation studies.

Comparative proteomics of paired vocal fold and oral mucosa fibroblasts

Injuries of the vocal folds frequently heal with scar formation, which can have lifelong detrimental impact on voice quality. Current treatments to prevent or resolve scars of the vocal fold mucosa are highly unsatisfactory. In contrast, the adjacent oral mucosa is mostly resistant to scarring. These differences in healing tendency might relate to distinct properties of the fibroblasts populating oral and vocal fold mucosae. We thus established the in vitro cultivation of paired, near-primary vocal fold fibroblasts (VFF) and oral mucosa fibroblasts (OMF) to perform a basic cellular characterization and comparative cellular proteomics. VFF were significantly larger than OMF, proliferated more slowly, and exhibited a sustained TGF-β1-induced elevation of pro-fibrotic interleukin 6. Cluster analysis of the proteomic data revealed distinct protein repertoires specific for VFF and OMF. Further, VFF displayed a broader protein spectrum, particularly a more sophisticated array of factors constituting and modifying the extracellular matrix. Conversely, subsets of OMF-enriched proteins were linked to cellular proliferation, nuclear events, and protection against oxidative stress. Altogether, this study supports the notion that fibroblasts sensitively adapt to the functional peculiarities of their respective anatomical location and presents several molecular targets for further investigation in the context of vocal fold wound healing.

BIOLOGICAL SIGNIFICANCE

Mammalian vocal folds are a unique but delicate tissue. A considerable fraction of people is affected by voice problems, yet many of the underlying vocal fold pathologies are sparsely understood at the molecular level. One such pathology is vocal fold scarring - the tendency of vocal fold injuries to heal with scar formation -, which represents a clinical problem with highly suboptimal treatment modalities. This study employed proteomics to obtain comprehensive insight into the protein repertoire of vocal fold fibroblasts, which are the cells that predominantly synthesize the extracellular matrix in both physiological and pathophysiological conditions. Protein profiles were compared to paired fibroblasts from the oral mucosa, a neighboring tissue that is remarkably resistant to scarring. Bioinformatic analyses of the data revealed a number of pathways as well as single proteins (e.g. ECM-remodeling factors, transcription factors, enzymes) that were significantly different between the two fibroblast types. Thereby, this study has revealed novel interesting molecular targets which can be analyzed in the future for their impact on vocal fold wound healing.

Control of the glottal configuration in ex vivo human models: quantitative anatomy for clinical and experimental practices

INTRODUCTION

The objective of this paper was to identify the determining factors of the glottal prephonatory configuration from the point of view of the resulting muscular actions (i.e., arytenoids adduction, membranous vocal fold adduction, and tension).

MATERIALS AND METHODS

21 human non-embalmed excised larynges (12 females and 9 males) were studied. Experiment A (11 larynges) studied four conditions of adduction of the vocal folds and arytenoids. Experiment B (10 larynges) studied the effect of cricothyroid approximation on the vocal fold length and the cricothyroid angle.

RESULTS

Experiment A: The mean glottal area significantly decreased from 41.2 mm² mean with no adduction, to 10.2 mm² mean with arytenoid adduction, to 9.2 mm² with membranous vocal fold adduction, and down to 1.1 mm² with the combination of arytenoid and membranous adduction. The effect of the task was statistically significant. Experiment B: The length of vocal folds increased from 13.61 mm median to 14.48 mm median, and the cricothyroid angle decreased of 10.05 median along with cricothyroid approximation.

DISCUSSION

The results of experiment A emphasize the sub-division of adductor intrinsic muscles in arytenoids adductors (i.e., LCA and IA), and membranous vocal fold adductor (i.e., TA). The results of experiment B quantify the effect of cricothyroid approximation on the vocal folds length. The implications of these results can be useful in both clinical practice and experimental studies.

MERS versus Standard Surgical Approaches for Porcine Vocal Fold Scarring with Adipose Stem Cell Constructs

OBJECTIVE

Cells, scaffold, and surgical approaches are important for regeneration of the lamina propria of the scarred vocal fold (VF). Microendoscopy of Reinke's space (MERS) is a surgical approach used to access the lamina propria. The present study evaluated MERS in the treatment of VF scarring as compared with standardized approaches for the treatment of VF scarring with adipose stem cell constructs.

STUDY DESIGN

Animal study.

SETTING

Academic center.

SUBJECTS AND METHODS

VF injury was performed bilaterally to induce scarring in 20 pigs. Eight weeks after injury, pigs were classified into no treatment, minithyrotomy, VF injection, VF incision/dissection, and MERS. All groups (except control) were implanted with adipose stem cell and hyaluronan. Four weeks after treatment, histology for collagen, hyaluronan, and fibronectin; mRNA expression for α-smooth muscle actin, tumor growth factor β1, collagen 1α1, collagen 3α1, matrix metalloproteinase 2, basic fibroblast growth factor, and hepatocyte growth factor; and tissue rheology were evaluated.

RESULTS

Differences were measured among surgical approaches for protein levels of collagen, hyaluronan, and fibronectin (P = .0133, P < .0001, and P = .0025, respectively). Fibroblast growth factor, collagen 1α1, and matrix metalloproteinase 2 transcript levels were different among treatment groups (P = .003, P = .0086, and P = .014, respectively), while no differences were measured for α-smooth muscle actin, tumor growth factor β1, hepatocyte growth factor, and collagen 3α1. Rheologically, significant differences were not measured between groups.

CONCLUSION

MERS is a promising surgical approach for the treatment of VF scarring, optimizing the placement of implanted biomaterials.

Nonstimulated rabbit phonation model: Cricothyroid approximation

OBJECTIVES/HYPOTHESIS

To describe a nonstimulated in vivo rabbit phonation model using an Isshiki type IV thyroplasty and uninterrupted humidified glottal airflow to produce sustained audible phonation.

STUDY DESIGN

Prospective animal study.

METHODS

Six New Zealand white breeder rabbits underwent a surgical procedure involving an Isshiki type IV thyroplasty and continuous airflow delivered to the glottis. Phonatory parameters were examined using high-speed laryngeal imaging and acoustic and aerodynamic analysis. Following the procedure, airflow was discontinued, and sutures remained in place to maintain the phonatory glottal configuration for microimaging using a 9.4 Tesla imaging system.

RESULTS

High-speed laryngeal imaging revealed sustained vocal fold oscillation throughout the experimental procedure. Analysis of acoustic signals revealed a mean vocal intensity of 61 dB and fundamental frequency of 590 Hz. Aerodynamic analysis revealed a mean airflow rate of 85.91 mL/s and subglottal pressure of 9 cm H2 O. Following the procedure, microimaging revealed that the in vivo phonatory glottal configuration was maintained, providing consistency between the experimental and postexperimental laryngeal geometry. The latter provides a significant milestone that is necessary for geometric reconstruction and to allow for validation of computational simulations against the in vivo rabbit preparation.

CONCLUSION

We demonstrate a nonstimulated in vivo phonation preparation using an Isshiki type IV thyroplasty and continuous humidified glottal airflow in a rabbit animal model. This preparation elicits sustained vocal fold vibration and phonatory measures that are consistent with our laboratory's prior work using direct neuromuscular stimulation for evoked phonation.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 126:1589-1594, 2016.

[3D visualization and analysis of vocal fold dynamics]

BACKGROUND

Visual investigation methods of the larynx mainly allow for the two-dimensional presentation of the three-dimensional structures of the vocal fold dynamics. The vertical component of the vocal fold dynamics is often neglected, yielding a loss of information. The latest studies show that the vertical dynamic components are in the range of the medio-lateral dynamics and play a significant role within the phonation process.

OBJECTIVES

This work presents a method for future 3D reconstruction and visualization of endoscopically recorded vocal fold dynamics.

MATERIALS AND METHODS

The setup contains a high-speed camera (HSC) and a laser projection system (LPS). The LPS projects a regular grid on the vocal fold surfaces and in combination with the HSC allows a three-dimensional reconstruction of the vocal fold surface. Hence, quantitative information on displacements and velocities can be provided. The applicability of the method is presented for one ex-vivo human larynx, one ex-vivo porcine larynx and one synthetic silicone larynx.

RESULTS

The setup introduced allows the reconstruction of the entire visible vocal fold surfaces for each oscillation status. This enables a detailed analysis of the three dimensional dynamics (i. e. displacements, velocities, accelerations) of the vocal folds.

CONCLUSIONS

The next goal is the miniaturization of the LPS to allow clinical in-vivo analysis in humans. We anticipate new insight on dependencies between 3D dynamic behavior and the quality of the acoustic outcome for healthy and disordered phonation.

Quantification of Porcine Vocal Fold Geometry

OBJECTIVE

The aim of this study was to quantify porcine vocal fold medial surface geometry and three-dimensional geometric distortion induced by freezing the larynx, especially in the region of the vocal folds.

STUDY DESIGN

The medial surface geometries of five excised porcine larynges were quantified and reported.

METHODS

Five porcine larynges were imaged in a micro-CT scanner, frozen, and rescanned. Segmentations and three-dimensional reconstructions were used to quantify and characterize geometric features. Comparisons were made with geometry data previously obtained using canine and human vocal folds as well as geometries of selected synthetic vocal fold models.

RESULTS

Freezing induced an overall expansion of approximately 5% in the transverse plane and comparable levels of nonuniform distortion in sagittal and coronal planes. The medial surface of the porcine vocal folds was found to compare reasonably well with other geometries, although the compared geometries exhibited a notable discrepancy with one set of published human female vocal fold geometry.

CONCLUSIONS

Porcine vocal folds are qualitatively geometrically similar to data available for canine and human vocal folds, as well as commonly used models. Freezing of tissue in the larynx causes distortion of around 5%. The data can provide direction in estimating uncertainty due to bulk distortion of tissue caused by freezing, as well as quantitative geometric data that can be directly used in developing vocal fold models.

Aerodynamic and acoustic effects of ventricular gap

PURPOSE

Supraglottic compression is frequently observed in individuals with dysphonia. It is commonly interpreted as an indication of excessive circumlaryngeal muscular tension and ventricular medialization. The purpose of this study was to describe the aerodynamic and acoustic impact of varying ventricular medialization in a canine model.

METHODS

Subglottal air pressure, glottal airflow, electroglottograph, acoustic signals, and high-speed video images were recorded in seven excised canine larynges mounted in vitro for laryngeal vibratory experimentation. The degree of gap between the ventricular folds was adjusted and measured using sutures and weights. Data were recorded during phonation when the ventricular gap was narrow, neutral, and large. Glottal resistance was estimated by measures of subglottal pressure and glottal flow.

RESULTS

Glottal resistance increased systematically as ventricular gap became smaller. Wide ventricular gaps were associated with increases in fundamental frequency and decreases in glottal resistance. Sound pressure level did not appear to be impacted by the adjustments in ventricular gap used in this research.

CONCLUSIONS

Increases in supraglottic compression and associated reduced ventricular width may be observed in a variety of disorders that affect voice quality. Ventricular compression may interact with true vocal fold posture and vibration resulting in predictable changes in aerodynamic, physiological, acoustic, and perceptual measures of phonation. The data from this report supports the theory that narrow ventricular gaps may be associated with disordered phonation. In vitro and in vivo human data are needed to further test this association.